On 5/28/19 4:44 PM, Paolo Carlini wrote:
Hi,
On 28/05/19 16:47, Jason Merrill wrote:
On 5/10/19 10:29 AM, Paolo Carlini wrote:
Hi,
a while ago Martin noticed that an unintended consequence of an old
tweak of mine - which avoided redundant error messages emitted from
cp_parser_init_declarator - is that, in some cases, we started
accepting ill-formed typeofs. Luckily, decltype isn't affected and
that points to the real issue: by the time that place in
cp_parser_init_declarator is reached, for a decltype version we
already emitted a correct error message. Thus I think the right way
to fix the problem is simply committing to tentative parse when,
toward the end of cp_parser_sizeof_operand we know that we must be
looking at a (possibly ill-formed) expression. Tested x86_64-linux.
The problem with calling cp_parser_commit_to_tentative_parse here is
that the tentative parse you're committing to is for the enclosing
scope, which is trying to decide whether e.g. we're parsing a
declaration or expression. If the operand of typeof is a well-formed
expression, and the larger context is an expression, this will break.
Better, I think, to commit and re-parse only if you actually encounter
an error.
Alternately, cp_parser_decltype_expr deals with this by using a
tentative firewall and CPP_DECLTYPE; cp_parser_sizeof_operand could do
the same, but that seems like a bigger hammer.
Today I spent quite a bit of time on this and eventually decided to
follow the example of decltype as closely as possible. Then I started
tweaking those drafts which laready passed the testsuite and after a
while ended up with the below, rather close to the current code, in
fact. Testing !cp_parser_error_occurred and in case calling
cp_parser_abort_tentative_parse by hand (closer to the decltype example)
also works. What do you think? Thanks, Paolo.
OK.
Jason
